In the .mm files use the crashpad::implicit_cast .. explicitly.

util/net/http_transport_mac.mm

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 185 matching lines @@
     }
     NSHTTPURLResponse* http_response =
         base::mac::ObjCCast<NSHTTPURLResponse>(response);
     if (!http_response) {
       LOG(ERROR) << "no http_response";
       return false;
     }
     NSInteger http_status = [http_response statusCode];
     if (http_status != 200) {
       LOG(ERROR) << base::StringPrintf("HTTP status %ld",
-                                       implicit_cast<long>(http_status));
+                                       crashpad::implicit_cast<long>(http_status));
       return false;
     }
 
     if (response_body) {
       response_body->assign(static_cast<const char*>([body bytes]),
                             [body length]);
     }
 
     return true;
   }
 }
 
 }  // namespace
 
 // static
 scoped_ptr<HTTPTransport> HTTPTransport::Create() {
   return scoped_ptr<HTTPTransport>(new HTTPTransportMac());
 }
 
 }  // namespace crashpad